A voltage converter is subjected to a feedback control such that its output voltage becomes coincident with a predetermined target voltage. For example, Japanese Patent Application Publication No. 2005-168129 describes a voltage converter including a voltage sensor that measures its output voltage. A controller of the voltage converter executes a feedback control such that a voltage difference between a target voltage and a measured output voltage becomes zero. For the convenience of description, a circuit that performs voltage conversion (a voltage converter circuit) may be referred to as a main circuit below. That is, the voltage converter includes the main circuit that performs voltage conversion and the controller that controls the main circuit.